MOT Fail - Emissions - 316i

[iDemonix]

Hi all,

My M40 engine'd 1994 316i Touring flew through it's MOT last year, and I even remember the tester remarking about how good the emissions were for its age.

Fast forward to this year, I've just failed. The car has done less than 1000 miles, and the only difference is it's been stood a couple of months without much use, and it now has E10 fuel in it (as during the panic buying that's all I could get before it ran out). It failed on:

Exhaust hydrocarbon content after 2nd fast idle exceeds manufacturer's specified limits (8.2.1.2 (a))
Exhaust Lambda reading after 2nd fast idle outside specified limits (8.2.1.2 (c))
Exhaust carbon monoxide content after 2nd fast idle exceeds manufacturer's specified limits (8.2.1.2 (a))

And the sheet looks like this:



The tester didn't really offer any advice other than "could be the E10 and it just needs a good long run" which obviously isn't doable without an MOT. I did have to swap the lambda sensor, but I did that before last years MOT. The exhaust did used to rattle a lot from what I presume is the catalytic converter (small box section, under the middle of the car), I just ignored it and eventually it became a lot quieter - could it be that the inner elements ended up breaking up and coming out of the exhaust? I'm hoping I don't need to source a replacement one of those as I had to have it modified (about 3x until it finally fit) to miss the steering column (pic below):



Any advice appreciated...

[iDemonix]

I think one of the things I'll try for the sake of it is replacing the lambda/o2 sensor, as the one I used was a cheap unbranded one as I couldn't find an OE type one... and I'm still struggling on that. RealOEM has the part number as 11781721125, but I was told the original would be a Bosch - but all the eBay ones are Denso or a brand I haven't heard of before, example:

https://www.ebay.co.uk/itm/143232903932

There's this Bosch one which lists fitting the M40B16 but doesn't have the part number anywhere on the listing...

https://www.ebay.co.uk/itm/294152492762

I've dug out the video of what it sounded like around the time of the last MOT:



I've just been out and repeated the same high-tech test, and it sounds absolutely solid now, with no rattle...

Also as I never throw anything out, I've still got the original lambda sensor, but the thread is gone which is why I replaced it, so not much chance of being able to reuse it:

[PattheCat]

Forgive me if you already know this, but I had my 1988 325i fail this year for emissions. I had to call F1 auto centre and ask them why they tested my 1988 car against the modern emissions test standard. It passed when they tested it again.

Basically, call up the MOT place and make sure that they haven't tried to do a modern test for emissions (holding the revs at a specified rpm). For older cars they just stick the probe in at idle and that's it.

[onthames]

I think one of the things I'll try for the sake of it is replacing the lambda/o2 sensor, as the one I used was a cheap unbranded one as I couldn't find an OE type one... and I'm still struggling on that. RealOEM has the part number as 11781721125, but I was told the original would be a Bosch - but all the eBay ones are Denso or a brand I haven't heard of before, example:

https://www.ebay.co.uk/itm/143232903932

There's this Bosch one which lists fitting the M40B16 but doesn't have the part number anywhere on the listing...

https://www.ebay.co.uk/itm/294152492762

I've dug out the video of what it sounded like around the time of the last MOT:



I've just been out and repeated the same high-tech test, and it sounds absolutely solid now, with no rattle...

Also as I never throw anything out, I've still got the original lambda sensor, but the thread is gone which is why I replaced it, so not much chance of being able to reuse it:

https://www.autodoc.co.uk/bosch/1148981

[fixedwheelnut]

Forgive me if you already know this, but I had my 1988 325i fail this year for emissions. I had to call F1 auto centre and ask them why they tested my 1988 car against the modern emissions test standard. It passed when they tested it again.

Basically, call up the MOT place and make sure that they haven't tried to do a modern test for emissions (holding the revs at a specified rpm). For older cars they just stick the probe in at idle and that's it.

This sounds like they have set the car up with the wrong parameters

https://www.gov.uk/guidance/mot-inspect ... tion-8-2-1

[iDemonix]

That's interesting, the flow chart makes it easier and for my next MOT I'll make sure I have a copy of it to hand!

Looking at the figures in that diagram though, I'd still have failed on CO! I've ordered that Bosch lambda sensor (thanks onthames) and will get that fitted, take it for a blast with some cleaner in the tank, and see how I get on. If that fails, I've found someone on the FB group with an old 316i exhaust they don't need. Would be a pain as I had to modify the exhaust to clear the Z4/Corsa steering linkage, but that's a last resort.

Will report back once new sensor is fitted and MOT is re-attempted....

[iDemonix]

New sensor arrived, went to remove the old one, and the state of it might explain a few things...



Most of the rest of it went inside the exhaust, so despite my hatred for the job, I removed it and the bits all instantly went through the cat and fell out the back (new vs. old):



The two things I skimped on during the build (everything else was Lemforder + Meyle) was the fuel pump and O2 sensor. Both failed me. Lesson learned.

I ended up taking the exhaust system off because the O2 sensor thread is stripped, and I could not get the Bosch one to tighten up as it started to ruin the new sensor, slipping after 1/2 a turn. When I originally took my exhaust off over a year ago, the original sensor from 1994 pretty much fell out, which is why it got replaced, and the replacement one never really sat right (or threaded all the way in).



Bit annoying, but I guess my options are now...

1. Figure out what size thread that should be, buy a tap, re-tap it, fit everything back to the car and hope with the new sensor it now passes. The issue with this is that I don't know the size/pitch etc of the thread, and if my cat is gone anyway, this will all be in vain.

2. Find a new 316i exhaust, hopefully with a working cat and non-stripped sensor thread, fit the new sensor to that, and then go through the faff of finding a local exhaust welder that can modify it in the same way as the current one, so it misses the Corsa steering linkage. Was a pain before as, like now, I couldn't get the car to a welder so it was a case of taking it to/from 2-3x and cutting/re-welding until it eventually fit.

Pic of the system where you can see one of the header pipes is modified a bit:



As it's back to being off the road, I'm in no real rush, so will have a think this weekend. If anyone has any suggestions, feel free to chip in. I'm tempted to attempt tapping if someone knows the dimensions, the internet seems to suggest that M18 x 1.5 is the standard (and to use a 'thread chaser' bolt type), as all that will cost me is the cost of a tap, a bit of time, and another £30 attempt at an MOT...

Potential tool: https://www.ebay.co.uk/itm/311620581002

[onthames]

Quick search and I found helicoil kits do exist for that size range but are rather expensive. The thread doesn't look too badly damaged. I think you may be able to get away with just getting the right size tap and retapping the hole to clean out the burs. If you contact bosch I'm sure they'll tell you the thread size and pitch and then you just need a tap and tap holder.

I'd add some sort of sealant when you put the sensor back in because of the damaged thread. Quick Google and it looks like Loctite 598 is suitible

[rix313]

I'd add some sort of sealant when you put the sensor back in because of the damaged thread. Quick Google and it looks like Loctite 598 is suitible

Can't say I've ever fitted a lambda sensor with loctite A good coating of copper grease is fine and will aid future replacement. I'd also suggest taking it to a classic freindly MOT station in future. Generic MOT monkeys don't know the rules so well when it comes to classic cars. Albeit it you 02 sensor was FUBAR but it shouldn't have been a failiure.

The thread doesn't look horrific. At least there is some there! Most Lambda sensors are M18 x 1.5mm thread. You can either buy a tap and carefully clean this thread up or there is the option to buy a new boss and have a new one welded on.

[iDemonix]

Thanks both.

I've ordered that M18 x 1.5 thread chaser, I'll give that a try, fit the new sensor, put the exhaust back on and re-attempt the MOT, I've found a better place to do the test.

If that fails then the only option is source another exhaust and deal with the modification faff again... hopefully not!

[onthames]

I'd add some sort of sealant when you put the sensor back in because of the damaged thread. Quick Google and it looks like Loctite 598 is suitible

Can't say I've ever fitted a lambda sensor with loctite A good coating of copper grease is fine and will aid future replacement. I'd also suggest taking it to a classic freindly MOT station in future. Generic MOT monkeys don't know the rules so well when it comes to classic cars. Albeit it you 02 sensor was FUBAR but it shouldn't have been a failiure.

The thread doesn't look horrific. At least there is some there! Most Lambda sensors are M18 x 1.5mm thread. You can either buy a tap and carefully clean this thread up or there is the option to buy a new boss and have a new one welded on.

598 is a silicone RTV that is exhaust and cat safe. If the threads aren't making a seal then their will copper grease stand up to that?

[martauto]

Seeing that the sensor has a small amount of thread, try grinding the tapped hole down with an angle grinder so you are using thread further down the hole and then try the new sensor to see if it bites any better .

Mart.

[iDemonix]

Seeing that the sensor has a small amount of thread, try grinding the tapped hole down with an angle grinder so you are using thread further down the hole and then try the new sensor to see if it bites any better .

Mart.

That's a good idea! If I hadn't already ordered the tool I'd give that a go, it should be here on Wednesday. If it doesn't work as intended I might try that though!

The exhaust on this car has been a pain in the arse from day 1

[martauto]

Seeing that the sensor has a small amount of thread, try grinding the tapped hole down with an angle grinder so you are using thread further down the hole and then try the new sensor to see if it bites any better .

Mart.

That's a good idea! If I hadn't already ordered the tool I'd give that a go, it should be here on Wednesday. If it doesn't work as intended I might try that though!

The exhaust on this car has been a pain in the arse from day 1

You can still try it anyway, belt and braces ?

Mart.

[iDemonix]

Seeing that the sensor has a small amount of thread, try grinding the tapped hole down with an angle grinder so you are using thread further down the hole and then try the new sensor to see if it bites any better .

Mart.

That's a good idea! If I hadn't already ordered the tool I'd give that a go, it should be here on Wednesday. If it doesn't work as intended I might try that though!

The exhaust on this car has been a pain in the arse from day 1

You can still try it anyway, belt and braces ?

Mart.

You've caught me on the one week where I've lent my angle grinder, and some other power tools, to a mate doing some welding! I should get that back Thu/Fri so it'll depend on the speed of Royal Mail vs. my mate's restoration skills for the car he's working on I'm still of the opinion I'm going to need to source a replacement cat anyway, but we'll see how it gets on.

Thanks for the help as always.

[rix313]

598 is a silicone RTV that is exhaust and cat safe. If the threads aren't making a seal then their will copper grease stand up to that?

The sensors have a crush sealing washer which would create a seal. If the thread is that damaged, effectively siliconing it in wouldn’t help anyway as you wouldn’t be able to tighten the sensor enough

[iDemonix]

As an update, I used martauto's suggestion of cutting off the top bit of knackered thread from the sensor hole, and fitted a new lambda. Filled the tank with some emissions cleaner type stuff, and gave it an Italian tune-up up and down the local A road en route to MOT bay.

Unfortunately whilst the hydrocarbon emissions were within tolerance, the carbon was 1.3% when it needed to be 0.3% - a vast improvement from around 6-7%, but not enough.

Bit the bullet and bought a new system, unfortunately I no longer have a welder so I just need to find someone local to cut them in half at the red line, and make a complete system. It'd be nice to get someone to modify the new system to clear the steering linkage, but it was such a pain to do last time without being able to take them the car, that I'll just get it cut + joined as below:

[martauto]

I used martauto's suggestion of cutting off the top bit of knackered thread from the sensor hole, and fitted a new lambda.

Just out of interest, did you have a good thread after this operation ??

Mart.

[iDemonix]

I used martauto's suggestion of cutting off the top bit of knackered thread from the sensor hole, and fitted a new lambda.

Just out of interest, did you have a good thread after this operation ??

Mart.

A bit, but not entirely.

I ended up buying an o2 sensor 'thread chaser' which is just a heavy duty tap with a bolt head. After failing to turn it by hand for an hour, I realised I wasn't really getting anywhere so I just absolutely rammed it in (and then out again) with an impact driver. After this, the new sensor went in, and I tightened it as much as I dared - I hope to never remove it again!

This is part of the reason I'd ideally like to re-do the down pipe mod, so I get a new o2 sensor hole, but it'll be much more of a pain than just chopping + cutting them so I'll likely go with that. Nipping to see an exhaust fab business down the road tomorrow.

[iDemonix]

Local fab shop charged me a tenner to cut the two systems, and sleeve the new one



Cut some slits on it and bought a clamp for £1.60 from Halfrauds



Before:



After:



She's road legal for another year!